Agkistrodon is a genus of pit vipers commonly known as American moccasins.[2][3] The genus is endemic to North America, ranging from the Southern United States to northern Costa Rica.[1] Eight species are currently recognized,[4][5] all of them monotypic and closely related.[6] Like all pit vipers, members of the genus are venomous. Common names include: cottonmouths, copperheads, and cantils.[7]
The name Agkistrodon comes from the Greek words ankistron (ἄγκιστρον, 'fishhook', with the irregular transliteration gk rather than the usual nk) and odon (ὀδών)[8] 'tooth'[9] and is likely a reference to the fangs.[7]
Some varieties of the genus are given the common name "moccasin" or "moccasin snake" in the United States, which is the Algonquian word for "shoe". The origin of this nickname is unknown. The first known use of "moccasin" to refer to a deadly venomous snake was in a 1765 publication. The nickname is used to refer to both cottonmouths and copperheads. According to the Word Detective, this use may be related to their color and appearance or the silence with which they move.[10] Another source for this name may be the Native American word "mokesoji" of unknown origin and meaning.[11]
Members of this genus have a number of features in common. All species have a relatively broad head with short fangs. A loreal scale is present, except in A. piscivorus. Usually, nine large symmetrical platelike scales are on the crown of the head, but in all species, these are often irregularly fragmented or have sutures, especially in A. bilineatus. All have a sharply defined canthus rostralis and a vertically elliptical pupil. Usually eight (6-10) supralabial scales and usually 10-11 (8-13) sublabials are present. The dorsal scales are mostly keeled and at midbody number 21-25 (usually 23), while A. piscivorus has 23-27 (usually 25). The snake has 127-157 ventral scales and 36-71 subcaudals. Of the latter, some may be divided. The anal scale is single. All have a color pattern of 10-20 dark crossbands on a lighter ground color, although sometimes the crossbands are staggered as half bands on either side of the body.[7]
The phylogeny of the species has long been controversial. Studies based on morphological[6] and venom characteristics[12] support the idea that A. bilineatus and A. contortrix are more closely related. However, an analysis of mitochondrial DNA,[13] as well as more recent molecular studies,[14][15] have concluded that A. bilineatus and A. piscivorus are sister taxa, with A. contortrix being a sister species to them both.[7]
They are found in North America from the northeastern and central United States southward through peninsular Florida and southwestern Texas, and in Central America on the Atlantic versant from Tamaulipas and Nuevo León southward to the Yucatan Peninsula, Belize, and Guatemala. They are seen along the Pacific coastal plain and lower foothills from Sonora south through Guatemala, El Salvador, Honduras, and Nicaragua to northwestern Costa Rica.[1]